Various already known processes are described in various publications.
In U.S. Pat. No. 3,018,273, a process for anionic polymerization of caprolactam is described in which an organomagnesium compound is used as a catalyst and a N-N diacyl compound as an activator.
U.K. Pat. No. 1,067,153 describes a process for the preparation of nylon block copolymers by polymerization of caprolactam in the presence of various types of activators. In the example, the application of an isocyanate-terminated polypropylene glycol as an activator and a potassium compound as a catalyst is described.
U.S. Pat. No. 3,862,262, U.S. Pat. No. 4,031,164, U.S. Pat. No. 4,223,112, U.S. Pat. No. 4,034,015, U.S. Pat. No. 3,925,325, U.S. Pat. No. 3,965,075 and U.S. Pat. No. Re. 30,371 describe various aspects in the preparation of activators used for polymerizing lactams and of the polymerization of lactam proper. More particularly, U.S. Pat. No. 3,862,262 describes lactam-polyol-acyl-polylactam block copolymers. U.S. Pat. No. 4,031,164 and U.S. Pat. No. 4,223,112 describe lactam-polyol-polyacyl lactam block copolymers having specific ratios of the several components. U.S. Pat. No. 4,034,015 relates to nylon block copolymers having at least 5 percent ester and group termination.
The other patents mentioned relate to the preparation of ester-amide compounds by condensation of alcohol and acyl lactam in the presence of catalysts of various types.
The European Patent Applications Nos. 67693, 67694 and 67695 relate to acyl-halide and acyl-lactam compounds and to a process for preparing nylon block copolymers therewith. The acyl-halide and acyl-lactam compounds are described by complex formulas.
The known systems on the basis of a high molecular weight activator, i.e. an activator obtained by reaction of a polyol with a compound containing activator groups, have the disadvantage that there is an upper limit to the molecular weight and the valency of the polyol. This is because, in order for the lactam polymerization to proceed well, a minimum concentration of activator groups relative to the amount of lactam is required.
As the molecular weight of the polyol becomes higher, the activator concentration will decrease. This makes it highly or totally impracticable to use a very high molecular weight polyol.